In the past, various types of electrical and/or electric-mechanical controls were utilized to control a winding circuit of a prime mover, such as for instance a dynamoelectric machine or an electric motor, with the winding circuit including main winding means and auxiliary winding means. Upon the energization of the prime mover, these past electrical controls were operable generally to effect the conjoint energization of both the main winding means and the auxiliary winding means during the starting mode operation of the prime mover, i.e., until a preselected speed thereof was attained. When the prime mover was energized to its preselected speed, the past electrical controls were operable to then render the auxiliary winding means generally ineffective in the winding circuit, and the main winding means continued to be energized during the running mode operation of the prime mover maintaining the preselected speed thereof. Of course, in the winding circuit of some prime movers, at least a part of the auxiliary winding means may be energized so as to assist the main winding means during the running mode operation of the prime mover, and capacitor means may be connected in the winding circuit in circuit relation with the main winding means and/or the auxiliary winding means.
In some of the prior art controls, when a rotatable assembly of the prime mover was energized to the preselected speed thereof, a centrifugal mechanism carried on the rotatable assembly was actuated to move an associated collar generally axially on the rotatable assembly from an at-rest position toward another position, and upon such axial movement to its another position, the collar drove linkage means for operating a switch which effected the deexcitation of the auxiliary winding means by disconnecting it from a power source. Thus, with the auxiliary winding means rendered ineffective in the winding circuit, the prime mover then was energized generally at the preselected speed during the running mode operation thereof in response to the continued excitation of the main winding means. Of course, at least one of the disadvantageous or undesirable features of the aforementioned centrifugal mechanism and associated linkage means is believed to be those well-known limitations attributable to most all mechanical devices, such as tolerance problems, wear problems, noise problems and, in some instances, reliability problems.
In another type of these prior art controls, only a current relay was employed for controlling the excitation of the auxiliary winding means. For instance, a coil of the current relay was serially connected in the winding circuit with the main winding means thereof, and contact means of the current relay was serially connected in the winding circuit with the auxiliary winding means thereof. When the prime mover was energized across the line, as previously mentioned, the coil of the current relay and the main winding means were excited, and the excitation of the relay coil effected the magnetic closure of the contact means of the relay so as to effect the excitation of the auxiliary winding means; therefore, in this manner, the main winding means and the auxiliary winding means were conjointly excited to energize the prime mover to generally to its preselected speed during a starting mode thereof. Of course, when the prime mover was so energized generally to its preselected speed, the current draw of the main winding means was appreciably reduced, and such reduction of current to a predetermined drop-out value of the relay caused the relay coil to weaken its magnetic affect thereby to permit the contact means of the current relay to return to their at-rest or open position. Thus, with the relay contacts so opened to interrupt current flow to the auxiliary winding means, the auxiliary winding means was rendered ineffective generally at the time the prime mover attains its preselected speed, and the prime mover remained energized generally at the preselected speed thereof during its running mode operation in response to the continued excitation of the main winding means. At least one of the disadvantageous or undesirable features of such past prime movers utilizing only a current relay for controlling excitation of the auxiliary winding means is believed to be that the contact means of the current relay had a tendency to weld in response to the generally large current draw by the auxiliary windings during the starting operation of the prime mover. Another disadvantageous or undesirable feature is believed to be that the current relay may have generated radio and television interference at the instant of make and break due to arcing of the contact means.
Another one of the prior art electrical controls for controlling the excitation of the auxiliary winding means was a positive temperature coefficient resistor (PTCR) which was connected in series with the auxiliary winding of the prime mover. When the prime mover was energized across the line, the main winding means and auxiliary winding means were initially conjointly excited since the PTCR exhibited little initial resistance to current flow to the auxiliary winding means. The PTCR acts generally as a low value resistor until its internal temperature reaches its "Curie" point or anomoly temperature at which time its resistance increases abruptly along with an increase of its temperature. Therefore, the temperature of the PTCR was increased in response to current flow therethrough to the auxiliary winding means during the starting operation of the prime mover, and generally at the time the prime mover attained its preselected speed, the resistance of the PTCR abruptly increased to a value appreciably limiting current flow therethrough. Thus, the auxiliary winding means was, in fact, rendered generally ineffective in the winding circuit generally at the time the prime mover attained its preselected speed, and the prime mover remained energized generally at the preselected speed thereof in response to the continued excitation of the main winding means. Of course, so long as the PTCR was energized, it remained "hot" exhibiting a high resistance to current flow, and it is believed that, under certain conditions, this may be a disadvantageous or undesirable feature. For instance, if for some reason the prime mover had not been energized to the preselected speed so that the torque of the main winding means alone would sustain such preselected speed, then it is believed that the prime mover might stall to zero speed and remain there since the PTCR would, in effect, block current flow to the auxiliary winding means. If the overload protection system of the prime mover did not alleviate the aforementioned stalled condition or locked rotor condition of the prime mover or if such overload protection system did not reset itself before the PTCR had time to cool, it is believed that this stalled condition of the prime mover would be perpetuated.
A combination relay and PTCR type electrical control is disclosed in copending application Ser. No. 829,276 filed Aug. 31, 1977 which is incorporated herein by reference, and a combination PTCR--overload protector device is disclosed in U.S. Pat. No. 4,042,860 issued Aug. 16, 1977 which is also incorporated herein by reference. Further, the William C. Rathje application Ser. No. 778,335 filed Mar. 17, 1977 (now U.S. Pat. No. 4,161,681 issued July 17, 1979) and assigned to the General Electric Company illustrates a prime mover having a relay device, an overload protector and a PTCR connected in circuit relation therewith, and this application is also incorporated by reference herein.